Corrosion resistant rocket nozzle

ABSTRACT

A corrosion resistant rocket nozzle for small rocket motors is disclosed. The rocket nozzle has a layer of hard anodize coating on the nozzle surface to reduce the effect of erosion during rocket burning. An ablative layer is placed over the anodize coating to produce a layer of cool gases alongside the nozzle walls during burning.

United States Patent [191 Garard et al.

[ 1 June 5,1973

CORROSION RESISTANT ROCKET NOZZLE lnventors: Richard S. Garard; WilliamJ. Mertens, both of Richmond, Ind.

Assignee: Avco Corporation, Richmond, lnd.

Filed: Sept. 21, 1970 Appl. No.: 73,738

U.S. Cl. ..239/265.l5, 60/200 A Int. Cl. ..B64d 33/04 Field of Search..239/265.15;

References Cited UNITED STATES PATENTS 12/1970 McAllister ,.239/265.l5

3,048,972 8/1962 Barlow ..239/265.15 3,253,403 5/1966 Hayes ..239/265.l53,313,488 4/1967 Lovingham ..239/265.15 X 3,194,013 7/1965 Dagneau et al..239/265.l5 UX Primary Examiner-Allen N. Knowles AssistantExaminer-John J. Love Attorney-Charles M. Hogan and Eugene C. Goodale [57] ABSTRACT A corrosion resistant rocket nozzle for small rocket motorsis disclosed. The rocket nozzle has a layer of hard anodize coating onthe nozzle surface to reduce the effect of erosion during rocketburning. An ablative layer is placed over the anodize coating to producea layer of cool gases alongside the nozzle walls during burning.

1 Claim, 4 Drawing Figures CORROSION RESISTANT ROCKET NOZZLE BACKGROUNDOF THE INVENTION This invention relates to nozzles and more particularlyto rocket nozzles having enhanced corrosion resistant qualities.

Small rocket motors are characterized by relatively expensive nozzles.Although the major portion of a rocket motor is well suited for massproduction techniques; generation of high temperature gases that mustflow under precisely controlled high pressure conditions require use ofexpensive materials in the nozzle area. In most cases, a high grade ofgraphite is used as a nozzle. This must be machined separately from themotor case and, through precise use of fitting and adhesive techniques,added to the motor body.

Ideally, a rocket nozzle would be machined directly in the aluminumrocket motor. Such a nozzle would be easier to control dimensionally andeliminate timeconsuming assembly. Bare aluminum, however, will notwithstand the hot gas flow without erosion and corrosion.

Accordingly, it is an object of this invention to provide an improvedrocket nozzle which overcomes the problems presently existing in similartype rocket nozzles.

SUMMARY OF THE INVENTION This invention provides an improved rocketnozzle having increased erosion and corrosion resistant qualities. Therocket nozzle has a first coating to substantially reduce the effects oferosion during burning and second coating over the first coating whichwill ablate during burning to produce a layer of cool gases which flowalongside the nozzle walls.

Other details, uses, and advantages of this invention will becomeapparent as the following description of the exemplary embodimentthereof presented in the accompany drawings proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE ILLUSTRATEDEMBODIMENT Reference is now made to FIG. 1 which illustrates oneexemplary embodiment of the corrosion resistant rocket nozzle of thisinvention, which is designated generally by the reference numeral 10.The nozzle member is provided with an annular inlet portion 12. In thepreferred form of this invention, the rocket nozzle is formed integrallywith the rocket body 14 which is manufactured preferably out of analuminum or an aluminum alloy. Although the rocket nozzle describedherein is integral with the rocket motor, it should be understood thatthe nozzle may be formed separately and have suitable means, such asthreads or the like thereon, to facilitate the attachment of the nozzleassembly to the body portion of the rocket.

The inlet portion 12 of the nozzle extends forwardly and blends into areduced throat portion 16 which, in turn, is integral with a generallyconically shaped outwardly flaring nozzle outlet section 18.

A hard anodize coating 20 is applied so as to cover the entire inletportion 12, reduced throat portion 16 and conical outlet portion 18 ofthe nozzle. The coating 20 is applied by any suitable process, such asby the Martin hardcoat process. This process produces a thick, dense,hard anodic coating on aluminum alloys. The hard coating consistsprincipally of aluminum oxide with the desired properties obtained bythickness and compactness of the coating. The aluminum oxide coating isa hard material which is also a good heat insulator and thus insulatesthe parent metal 14 for a short time. However, during firing or burningof the rocket, the temperature of the coating 20 increases quite rapidlyand the heat is conducted to the parent metal 14. The heat conducted tothe parent metal or nozzle 14 permits the coating 20 to be burned off bythe gas stream at which point erosion of the parent metal 14 occurs. Itcan be seen that the coating 20 is porous and uneven on the side exposedto the high temperature gas. The rough condition of the coating surfacegenerates turbulent gas flow thereby accelerating erosion. v

To overcome this disadvantage of the coating 20, a high temperatureenamel 22 is applied over the hard coating 20, as seen in FIG. 2, on allsurfaces which are subjected to gas flow. A smooth surface is createdover the entire nozzle area which is subjected to the high temperaturegases with an increased reservoir of enamel being on the upper end ofthe nozzle, i.e'., the reduced throat portion 16 and inlet portion 12.

High temperature enamel 22 which has'been used with good results isDuPont DuluxNo. 631-89, blue engine enamel. The enamel performs twodistinct functions in this invention. The first is that the enamel 22fills the voids and cavities in the aluminum coating 20 so as to producea smooth surface to be exposed to the high temperature gases. Inaddition, the enamel is heat resistant and during the burning of therocket, the enamel will ablate so as to produce a layer of cool gasesthat flow alongside the nozzle walls.

Referring now to FIG. 3, the nozzle 10 is shown during the initial burnconditions. The smooth surface provided by the enamel 22 allows uniformflow of high temperature gases, shown generally by 24, during theinitial burn. Thereafter, as the surface temperature of the enamel 22rises, the enamel 22 will begin to ablate which produces relatively coolgases 26 which are added to the high temperature gas flow. Since thecooler gases 26 form on the entire'surface coated by the enamel 22 atthe inlet end, the gases would tend to remain along the surface of thenozzle as seen in FIG. 4 which illustrates the maximum gas flow duringthe rocket burning. Thus, the cool layer of gas 26 shields the coating20 from high temperature gases as both the high temperature gas 24 andcool gas 26 are accelerated out of the rocket. The shielding effect ofthe cool gases helps to keep the temperature of the coating 20sufficiently low to prevent burn off of the coating. Thus, with thecoating 20 remaining, corrosion or erosion of the parent metal 14 isprevented. The thickness of the high temperature enamel is designed suchthat sufficient cool gases are produced continuously throughout theburning time. Variations of this thickness are thereby a function of thecharacteristic burning time and flame temperature of the particularpropellant being used.

Thus it can be seen that a rocket motor nozzle may be produced and usedduring the rocket burning with out the normally required carbon insert.

While a present exemplary emobidment of this invention has beenillustrated and the method of producing the invention has beendescribed, it will be recognized that this invention may be otherwisevariously embodied and practiced by those skilled in the art.

What is claimed is:

l. A rocket nozzle having an improved corrosion resistant qualitycomprising:

a nozzle member defining an inlet portion, a reduced throat portion andan outlet portion;

a hard anodize coating on the inner surface of said nozzle member; and

a high temperature enamel ablative coating applied over said hardanodize coating at least covering the entire inlet portion and throatportion, said enamel coating being of greater thickness at the nozzleinlet portion and reduced throat portion wherein said ablative coatingis in contact with the high temperature gases of the rocket duringburning whereby ablation of the enamel coating upstream of the throatportion produces a layer of cool'gases which flows between the hightemperature gases and theanodize coating and acts as a moving insulatortherebetween.

1. A rocket nozzle having an improved corrosion resistant qualitycomprising: a nozzle member defining an inlet portion, a reduced throatportion and an outlet portion; a hard anodize coating on the innersurface of said nozzle member; and a high temperature enamel ablativecoating applied over said hard anodize coating at least covering theentire inlet portion and throat portion, said enamel coating being ofgreater thickness at the nozzle inlet portion and reduced throat portionwherein said ablative coating is in contact with the high temperaturegases of the rocket during burning whereby ablation of the enamelcoating upstream of the throat portion produces a layer of cool gaseswhich flows between the high temperature gases and the anodize coatingand acts as a moving insulator therebetween.